This invention relates to pickup tubes having a field mesh support electrode adjacent to one end of a focus electrode and more particularly to a vidicon type camera tube having an improved means for locating the mesh support electrode relative to the focus electrode so that the focus electrode and the mesh support electrode are mutually parallel, concentric and electrically insulated.
One of the several known types of pickup tubes is known generally as a vidicon and generally comprises an evacuated tubular envelope enclosing an electron gun and a target electrode. The target electrode may include a silicon wafer or another photoconductive target supported by a transparent support member, which normally is an optically clear transparent faceplate sealed to the end of the envelope. Closely spaced from the target electrode, facing the electron gun, is a fine mesh screen or beam decelerating mesh electrode. A hollow tubular focus electrode is disposed between the electron gun and the mesh screen. A cylindrical mesh support electrode retains the mesh in spaced relation to the focus electrode.
The operating characteristics of the camera tube will be adversely affected if the mesh support electrode is not electrically insulated from, concentric with, and parallel to the focus electrode. Support structures for locating the mesh support electrode vis-a-vis the focus electrode are disclosed in the U.S. Pat. No. 3,073,981, issued on Jan. 15, 1963 to L. D. Miller et al., entitled "Photoconductive Pickup Tube Having an Electrically Isolated Mesh Assembly." These structures require the accurate location of a plurality of precision parts; however, such parts are expensive and increase the manufacturing cost of the tube. By way of example, the above-mentioned patent discloses two embodiments; one embodiment requires four precision parts while the other requires seven. It is, therefore, desirable to reduce the number of precision parts without adversely affecting the performance of the tube. The term precision part as used herein means a part having at least one dimension held to a tolerance of plus or minus 0.003 inch (0.0762 mm).